The present invention relates to a method and apparatus for reclaiming spent aqueous glycol solutions used as heat transfer fluids; for example, automotive antifreeze, and in particular to a method and process which is mobile allowing centralized processing of the spent glycols and centralized regeneration and waste management.
The disposal of spent aqueous glycols is a major problem today, particularly in the case of spent automotive antifreeze solutions. Spent antifreeze solutions, for example, are severely contaminated with particulate materials, such as engine rust particles, oil and grease, and dissolved minerals, including heavy metals which are toxic and hazardous to the environment. Even spent solutions, however, contain usable glycols which are desirable to recycle.
In addition to cleaning the contaminants from the spent antifreeze, recycled antifreeze, in order to be reusable, must be adjusted to the correct concentration of glycol and must have certain additives, such as corrosion inhibitors, replenished.
The final problem with reprocessing spent glycols, particularly used automotive antifreeze, is that used automotive antifreeze is collected at dispersed locations, such as garages, service station and other vehicle maintenance facilities. Small package systems have been introduced to meet this need for processing at the source of the spent antifreeze, but such systems are inherently less efficient than centralized processing facilities. Furthermore, waste disposal is a problem, since some of the waste generated from the cleaning of spent antifreeze may be hazardous from the concentration of heavy metals or other contaminants. (Heavy metals could include lead, arsenic, zinc, copper, and chromium. Other dissolved metals not usually included in the category of heavy metals, such as aluminum, are also found in spent glycol and must be removed as a waste.) It is impractical, for example, for a service station, to acquire a hazardous waste treatment and disposal permit. It is therefore desirable to provide for a method and apparatus to treat spent glycol solutions near the source of the spent glycol while providing the benefits of centralized processing and waste disposal.
Various patented processes are known that use filtration to purify spent antifreeze or other heat transfer fluids. The prior art discloses the use of mechanical filters, centrifuges, ultrafiltration and reverse osmosis. In addition, a number of patents disclose the use of anion and/or cation resins. Furthermore, a number of patents disclose the use of activated carbon for purifying spent glycols or heat transfer fluids.
An example is U.S. Pat. No. 5,422,008 and the closely related U.S. Pat. No. 5,223,144, both of which relate to cleaning recycled antifreeze solutions. They disclose the use of mechanical filters to remove particles down to five microns in size followed by activated carbon, chemical precipitation and ion exchange (anion and/or cation). The use of mechanical filtration down to 0.2 microns in size is suggested as well. These patents disclose small package systems of the type applicable to a single small user. These processes include the step of chemical precipitation which may be undesirable as producing excessive waste for disposal. Further neither suggests the use of ultrafiltration membranes as opposed to mechanical filtration.
To the knowledge of the inventors of the present invention, the prior art does not suggest the desirability of using a mobile facility for processing spent automotive antifreeze, allowing centralized processing and waste disposal. U.S. Pat. No. 5,160,443 discloses the use of an apparatus transportable by a van for recycling contaminated industrial liquids. The particular processing steps disclosed in this patent include the use of fine screen filters and a centrifuge to remove particulate material. The filtering step is then followed by the step of introducing additives to the filtered material. This patent does not disclose the use of ultrafiltration, activated carbon or ion exchange.
These and other disadvantages and limitations of the prior art are addressed by the apparatus and method of the present invention as described below.